In general, graphite is a raw material formed of overlapped layers of planar macromolecules, in which hexagonal rings consisting of carbon atoms are infinitely connected with each other while forming sheets. Including good electric conductivity, the graphite has lubricant properties and flexibility contributed to a lamella structure of the macromolecule (polycene). Further, although the graphite is easy to break, it has a low reactivity since it is a macromolecule.
Since the carbon sheets of the graphite having the polycene structure are joined to each other by van der Waals forces, the distance of 14.2 nm between the carbon sheets is larger than the distance of 35.5 nm between the carbon atoms. Thus, an intercalation compound can be formed by insertion of other atoms into a gap between the carbon sheets. Specifically, with a net plane of the graphite crystal maintained, a great quantity of atoms, molecules or ions are inserted into the gap between the sheets, thereby forming the intercalation compounds.
That is, when an intercalation compound or remnant compound with an acid, such as sulphuric acid, applied between the sheets of the graphite is rapidly heated to a temperature of about 1000° C., the acid between the sheets is vaporized to generate gas, and the interlayer of the graphite expands dozens or hundreds of times due to an expansion pressure of the gas, thereby forming the intercalation compound, what is so referred to as “expanded graphite.”
A conventional method of manufacturing expanded graphite products will now be described with reference to FIG. 1.
First, since the expanded graphite has a density 1/50˜ 1/200 times smaller than that of a general graphite, expanded graphite is laminated to a predetermined height, considering a thickness and a density of an expanded graphite sheet to be formed with expanded graphite (S2). For example, when forming a 5 mm thick expanded graphite sheet using expanded graphite of a density 1/200 times smaller than that of the general graphite, expanded graphite is laminated to a height 200 times or more of 5 mm.
Then, expanded graphite laminated to a predetermined thickness is compressed with a high capacity press (S4) and rolled with a roller, to form a high density, expanded graphite sheet (S6). The expanded graphite sheet is formed into a desired shape through additional mechanical processes, such as cutting or shaping, (S8), completing the manufacturing process for the expanded graphite product (S10).
However, the conventional method of manufacturing the expanded graphite products has problems in that as the expanded graphite products increase in thickness, expanded graphite should be laminated higher when manufacturing the expanded graphite product, thereby not only increasing the capacity of a press, but also making equipments huge due to requirement of continuous rolling equipment. Further, expanded graphite having a considerably low density is compressed, rolled and formed in a great quantity, so that it is very difficult to increase the density and to achieve a uniform density.
Further, according to the conventional method, expanded graphite of the considerably low density is compressed, rolled and formed in a great quantity, so that space in expanded graphite is not completely removed. Thus, not only does expanded graphite have a non-closely packed structure so that mechanical properties, such as tensile strength, compression strength, hardness or the like, are poor, but also does expanded graphite have a directional preference due to the compression process and may be formed only into the sheet shape, so that a final shape is restricted.